When in the railroad station Asta runs after the other dog and then sits down; his leash is curled up in front of him. However, on the next cut, the leash is now straightened out behind him.
When Mary is holding her rifle up over her shoulder as if about to hit Nick Charles and then reacts to the mention of the name Eleanor Morgan; she lowers it. However, in the next cut after Nick acknowledges knowing about Eleanor; the rifle is still raised over her shoulder, and then she repeats the action of lowering it.
When Nick places Mrs. Draque on the bed; she has her legs off to the side of the bed. However, on the next cut, her legs are flat on the bed.
Just after Nick and Nora meet Mrs. Peavy and Willoughby in front of his parent's house, a group of kids are shown running up to the fence as the Peavys walk away. They appear to be chatting with Nick and Nora, yet when the scene cuts back to Nick and Nora they are sitting back down in their respective hammock and chair and the kids are nowhere to be seen.
In the baggage car scene, Asta twice hides behind a milk can - once running from the right and the second time, running from the left. In the second sequence, the writing on the crates behind him is backwards. This is because the film editor simply reversed the negative from the first sequence in order to "create" the second. [Note: though, in the novel, Asta was a female schnauzer, in the movies, the dog is a male wire fox terrier.]
When Nick and Nora are in the baggage car, the train passes a windmill. The scene outside is being shown on a rear-screen projection, but the camera shooting it oddly and obviously pans when passing said windmill.
It has been said that the rifle in the film was a Bren gun and not a Japanese weapon. However, the Nambu machine gun looks very much like a Bren gun. The stock is the most easily spotted give-away. The Bren gun's stock come straight back from behind the pistol grip right behind the trigger guard, while the Nambu's stock has a slight drop to it, right behind the pistol grip. The gun in this film is, in fact, a Japanese Nambu machine gun.
When Nick is repairing the table he does a couple of counter clockwise turns and then one slow, firm counterclockwise turn, seemingly making the screw very tight. This was intentionally tongue in cheek, as one must turn a screw clockwise to tighten it..
In the gift shop scene, Willie Crump, played by Donald Meek, has an obvious rip in the sleeve hem of his jacket, on the back right shoulder. His white shirt shows through. It can be seen as he gets up from having his head inside the display case.
When Brogan is sitting with Nick's parents at the table, he is describing a card announcing births. During his description, he takes a bite of cake, but the dialog continues non stop, even though his mouth is obviously not mouthing the words.
When Peter Berton is standing in the doorway talking to Nick, when he speaks, the words come out, "You see, there's something I've gotta get off my mind." But the mouth movements indicate he said, "There's something I've gotta get off my chest."
At the very end of the film Hilda the maid asks Nick for his autograph. She hands him a pad to sign and it looks like the film rewinds or it was not edited properly and appears she pushes it toward him and he pushes it back to her.